Numerous designs are already known in practice, wherein for compacting the fiber material (fiber strand) discharged by a drafting system unit, a compaction unit is situated downstream. Following such a compaction unit, the compacted fiber material, after passing through a nip point, is fed to a twist generation device. Such a twist generation device in a ring spinning machine, for example, is composed of a traveler that revolves on a ring, and the yarn produced is wound onto a rotating bobbin. Suctioned revolving, perforated suction drums or revolving aprons provided with perforations are essentially used as compaction units. A specialized suction area on the compaction element is thus defined by using appropriate inserts inside the suction drum or inside the revolving apron. These types of inserts may be provided, for example, with appropriately shaped suction slits to which a negative pressure is applied, thus generating a corresponding air flow at the periphery of the particular compaction element. In particular, protruding fibers are incorporated as a result of this air flow, which is oriented essentially transversely with respect to the direction of transport.
These types of devices have been illustrated and described in the publications EP 947 614 B1, DE 10 2005 010 903 A1, DE 198 46 268 C2, EP 1 612 309 B1, DE 100 18 480 A1, and CN 1712588 A, for example. These cited publications essentially involve fixedly mounted compaction units which are installed following the particular drafting system. The drive of these compaction units is sometimes achieved via specialized drive shafts that are situated over the length of the spinning machine and that are in drive connection with either a suction roller or a revolving apron. Likewise, the drive of the compaction unit may be achieved via a fixedly mounted drive connection to pressure rollers that rest on the compaction unit and by means of which the drive is transmitted to the compaction unit via friction. Furthermore, examples of drives are found in the exemplary embodiments of the cited publications, wherein the drive of the compaction unit is achieved via additional drive elements of the top and bottom rollers of the pair of delivery rollers of the drafting system unit.
Designs are also known in which conventional drafting systems may be retrofitted with such a compaction device. One such example is found in DE 102 27 463 C1, for example, in which the punch of the drafting system unit is extended in order to support an additional drive roller provided for the drive of the retrofitted compaction device, which is likewise supported on this extension. The drive roller extends over the entire length of the spinning machine.
A design is known from CN 101613896 A in which an additional element is screwed to the punch for extending the punch of the drafting system. Also described in this exemplary embodiment is a gearing stage having gear pairs via which the drive of an additional compaction device is to be achieved. This device is also relatively complicated to install and inflexible regarding the selection of certain gear ratios.
In practice, it is necessary, depending on the fiber material to be processed and the design of the compaction device, to adapt the peripheral speed of the compaction element (revolving suction drum or apron) to the peripheral speed of the pair of delivery rollers of the drafting system in order to obtain the desired compacting of the yarn. This also depends largely on the geometry of the suction slit used inside the compaction element. In many cases it is advantageous for the peripheral speed of the compaction element to be less than the peripheral speed of the delivery rollers of the drafting system in order to obtain compression of the material in the area of the suction slit. In other cases, the converse is advantageous.
A design of a compaction device is known from DE 100 50 089 C2 which is provided for retrofitting of a conventional drafting system unit. A device is proposed that allows the drafting system unit to be retrofitted with a compaction device without additional drive members. Different designs of compaction devices are disclosed in the exemplary embodiments of the cited publication. For its drive, this compaction device lies, for example, with a partial area of its periphery on the driven top roller of the pair of delivery rollers of the drafting system unit. In another disclosed design, deflection rollers connected to the compaction device are in frictional contact with the top roller of the pair of delivery rollers of the drafting system unit in order to accept the drive from the top roller.
A certain gear ratio may be specified by use of this drive device. That is, a gear multiplication or gear reduction may thus be specified. However, if it is necessary to change the gear ratio (for example, when the fiber material is exchanged), this drive device is inflexible and requires a greater expenditure of time to make this change.